SiC has a larger energy band gap compared with Si, so various technologies for production of high grade SiC single crystal suitable as a semiconductor material etc. has been proposed in Japanese Unexamined Patent Publication (Kokai) No. 2003-300797, Japanese Unexamined Patent Publication (Kokai) No. 2003-300796, Japanese Unexamined Patent Publication (Kokai) No. 2003-342099, Japanese Unexamined Patent Publication (Kokai) No. 2001-181095, Japanese Unexamined Patent Publication (Kokai) No. 10-17399, etc.
However, the above technologies had the following problems:
(1) Crystal defects degrading the semiconductor device properties (stacking faults, triangular-defects, and other surface defects) easily occurred.
(2) The rate of crystal growth was slow.
(3) The flatness of the epitaxial crystal growth plane (surface morphology) was poor
In particular, prevention of the surface defects of the above (1) is a major premise for practical use as a semiconductor material.
As has been known in the past, if making the SiC (0001) plane (bottom plane of hexagonal crystal) the epitaxial growth plane, SiC crystals (polygonal) with different crystal structures will easily become mixed in the growth plane and high quality crystal cannot be obtained.
Therefore, step flow growth has been performed making the growth plane an angle inclined by several degrees from the (0001) plane (off-angle). However, even if adopting this method, it was extremely difficult to completely avoid the occurrence of defects critical to the device properties such as triangular defects or carrot defects (device killers) and achieve stable epitaxial growth.
The reason for this is believed to be that in step flow growth, the crystal growth proceeds in steps in the lateral direction. With substrates with small off-angles, however, the terrace area is large, so starting points of defects easily arise on the terrace surfaces and the defects grown from those starting points are taken into the epitaxial growth layer. Further, pinholes due to large spiral dislocations called “micropipes” extending in the <0001> axial direction are also passed on to the growth layer.
As opposed to this, the practice has also been to make the (11-20) plane the growth plane. While the occurrence of micropipes can be avoided, a large number of stacking faults end up being included. This becomes a cause for deterioration of the device properties.
To solve this problem, Japanese Unexamined Patent Publication (Kokai) No. 2003-300797 discloses to make a plane inclined from the (11-20) plane by an off-angle of at least 3 degrees to not more than 60 degrees in any direction in the range of −45 degrees to 45 degrees in the <1-100> axial direction centered about the <0001> axis the epitaxial thin film growth plane. This improves the growth rate of the SiC single crystal, but has the problem that the influx of impurities cannot be reduced.
In particular, a method of crystal growth solving the above problems has been sought for 4H—SiC single crystal, the crystal polyhedron most suitable as a semiconductor material from the viewpoint of the device properties.